Nitrogen, water may help injured oak trees

Published 5:13 am, Wednesday, July 25, 2012

Dear Neil: What can I do to help oak trees whose roots were cut during trenching in our yard last summer? They are sparse, and their color is not as vibrant.

Answer: All you can do at this point is supply nutrition and water. Nitrogen is critical for production of leaves, but you don't want to overdo it this year, because the root loss is still relatively recent. I'd suggest adding half of a pound of nitrogen per inch of trunk diameter. Spread it uniformly over the root system. Water the trees deeply after the feeding and every week the rest of the summer and early fall.

Dear Neil: I have lost half of my elaeagnus plants. Parts of the plants die, but I've had it before, and it usually takes the entire plant. What causes that?

Answer: I've been around elaeagnus almost all of my life, and the times I've seen the kind of dieback your photos showed usually have been associated with a traumatic drought. There has been a great deal of this damage across Texas over the past 18 months. Sometimes it seems to take a few extra months to develop. Also, they are susceptible to cotton root rot when they're in alkaline soils, but it kills the entire plant at the same time. Those are the only two problems I have seen bother them.

Dear Neil: Our garden has not been productive this year. We built raised beds and used a variety of materials (compost, purchased soil, etc.). We have had poor fruit set on our zucchini and summer squash. Butternuts were small, as were our Roma tomatoes. We fertilize with 8-8-8, and we water daily. What could be wrong?

Answer: It's hard to tell just from those facts. Hopefully you planted your crops early enough for them to mature before the heat of summer. It sounds like they also may have needed more nitrogen than the 8-8-8 fertilizer would have supplied. Have the soil tested, and don't be surprised if the results call for a high-nitrogen or all-nitrogen plant food, even for flowering and fruiting vegetables. The crops you mentioned should have been planted soon after the average date of the last killing freeze.

Dear Neil: We have a collection of very aggressive weeds growing in our yard. They look somewhat like maples. What are they, and how can I stop them?

Answer: I normally don't do plant IDs here because they don't mean much to all the other readers, but you have a very common volunteer tree, and it may surprise you. This is juvenile foliage of mulberry trees. As they grow taller, the lobed leaves will give way to rounded leaves without lobes (typical mulberry leaf shape). These are seedlings of a fruiting mulberry, and they, too, eventually will produce fruit. You can either hoe them out, or, in open spaces, you can apply a broadleafed weedkiller.

Dear Neil: We have a 12-year-old red oak that always has been lush. This year, the foliage is sparse, and there is a big acorn crop. Is the thin foliage because of the drought?

Answer: Yes, unless there are other issues that have cropped up with it in the past 15 months. For the record, I received a very similar letter from someone with a walnut tree question, also related to drought. Anyone who has a tree that did well for many years, and then developed a problem after last summer, needs to suspect drought damage first and foremost.

Dear Neil: Why would my latest tomatoes be hard? The first crop was just fine. Should I replant for fall?

Answer: That's the way tomatoes behave in the hottest of summer weather. Fruit quality just about goes out the window. Fall plantings need to be made in late June or early July in North Texas and by mid-July for South Texas. There's no way to know when it's too late, because we don't know when the first frost will happen.

Dear Neil: What would kill an apricot tree almost overnight? I have another tree that is still healthy.

Answer: It could have been a massive attack of peach tree borers. Check the lower trunk, just above the ground line, for globs of congealed sap coming out of the borers' tunnels. Unfortunately, there is no reliable way of getting them out of a tree. It's even difficult to keep them out of the trunk in the first place. The other possibility would be the soil-borne fungus called cotton root rot. It's present in alkaline soils, and it behaves exactly as you described. Hopefully it won't migrate within the soil to attack the other tree. Adding large quantities of sulfur soil acidifier might help protect the surviving tree, but results aren't always perfect.

Dear Neil: I have 21 variegated Chinese privets I planted last year. Regular privet is invading some of their stems. How can I prevent it?

Answer: You have to prune it out. The variegated character is not a stable gene. It's quite common for them to revert.